LEXINGTON, Neb. -- A 25-year-old female Nebraska school teacher was in custody in California Tuesday, charged with taking a 13-year-old male student to Mexico for sex.

An FBI affidavit claims Kelsey Peterson and the unidentified youth fled Lexington, Neb., on Oct. 26, a day after Peterson was suspended for suspected unprofessional conduct involving the boy, USA Today reported.

The pair were located Friday in the Mexican border city of Mexicali after the boy text-messaged family in Nebraska, investigators said. Peterson appeared in federal court in El Centro, Calif., Monday to face charges of transporting a child across state lines or a foreign border for sexual activity, and also faces state charges of kidnapping, child abuse and contributing to the delinquency of a minor, prosecutors told the newspaper.

The youth is considered an illegal immigrant, and will not be able to return to the United States, where he has lived most of his life, Dawson, Neb., County Attorney Elizabeth Waterman said.

He could return to act as a witness for the prosecution, but would have to return to Mexico as soon as the trial ended, Waterman said.